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Mingwu Wang, Jing Li, Fayez Ghishan, Hua Xu; NHE8 Participates in Electrolyte and Water Secretion in Conjunctival and Lacrimal Gland Epithelia. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2109.
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NHE8 is a membrane protein in the sodium/hydrogen exchanger (NHE) family. It involves mucin and bicarbonate secretion in the intestine. But it is not known if NHE8 is expressed in conjunctival and lacrimal gland tissues, and what role it may play in maintaining ocular surface homeostasis.
The study was conducted in compliance with the Tenets of the Declaration of Helsinki and ARVO statement for the use of animals in Ophthalmic and Visual Research. Mouse conjunctival and lacrimal gland tissues were harvested for immunohistochemistry, total RNA extraction, and protein isolation. Age- and gender-matched wild type (WT) and NHE8 knockout (KO) mice (eight in each group) were subjected to examiner-masked ocular surface evaluations including tear pH measurement with narrow range pH paper, and under anesthesia, phenol cotton thread test, tear break up time (TBUT), and corneal fluorescein staining.
The expression of NHE8 was confirmed at both mRNA and protein levels in conjunctival and lacrimal gland tissues. Immunohistochemistry staining showed that NHE8 was located on the membrane of both epithelial and goblet cells of conjunctiva. In lacrimal gland, NHE8 is differentially expressed on cell membrane, with only certain gland acinar and ductal epithelial cells being positive. Tear pH value of KO mice was lower than that of WT mice (p < 0.001). KO mice also had significantly lower phenol cotton thread test, TBUT, and significantly higher corneal staining scores (p < 0.05, respectively).
For the first time, we have demonstrated that NHE8 is involved in ocular surface pH regulation. Mice lacking NHE8 function showed signs of dry eye. Our results shed new insights into the understanding of dry eye syndrome, which could lead to new therapeutic strategies.
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